Streptococcus pneumoniae is a gram positive bacteria which is a major cause of invasive infections such as sepsis, meningitis, otitis media and lobar pneumonia (Tuomanen et al NEJM 322:1280-1284, 1995). Pneumococci bind avidly to cells of the upper and lower respiratory tract. Like most bacteria, adherence of pneumococci to human cells is achieved by presentation of bacterial surface proteins that bind to eukaryotic carbohydrates in a lectin-like fashion (Cundell, D. & Tuomanen, E. (1994) Microb Pathog 17:361-374). Pneumococci bind to non-inflamed epithelium, a process that can be viewed as asymptomatic carriage. It has been proposed that the conversion to invasive disease involves the local generation of inflammatory factors which, activating the human cell, change the number and type of receptors available on the human cells (Cundell, D. et al. (1995) Nature, 377:435-438). Presented with an opportunity in this new setting, pneumococci appear to take advantage and engage one of these unregulated receptors, the platelet activating factor (PAF) receptor (Cundell et al. (1995) Nature, 377:435-438. Within minutes of the appearance of the PAF receptor, pneumococci undergo waves of enhanced adherence and invasion. Inhibition of bacterial binding to activated cells, for instance by soluble receptor analogs, blocks the progression to disease in animal models (Idanpaan-Heikkila, I. et al. (1997) J. Infect. Dis., 176:704-712). Particularly effective in this regard are soluble carbohydrates containing lacto-N-neotetraose with or without an additional sialic acid which prevent pneumococcal attachment to human cells in vitro and prevent colonization in the lung in vivo.
Choline Binding Proteins: Candidate Structural Adhesin Gene:
Pneumococci produce a family of surface proteins capable of binding to the bacterial surface by non-covalent association to the cell wall teichoic acid or lipoteichoic acid. The surface of Streptococcus pneumoniae is decorated with a family of CBPs (Choline Binding Proteins) that are non-covalently bound to the phosphorylcholine. CbpA, is an 75 kD surface-exposed choline binding protein that shows a chimeric architecture. There is a unique N-terminal domain a proline rich region followed by a C-terminal domain comprised of 10 repeated region responsible for binding to choline.
CbpA, is an adhesin (ligand) for the glycoconjugate containing receptors present on the surface of eucaryotic cells. Mutants with defects in cbpA showed reduced virulence in the infant rat model for nasopharyngeal colonization. This binding is directed to choline determinants which decorate the teichoic acid and is mediated by a signature choline binding domain in each of the members of this family of proteins. The choline binding domain was discovered and fully characterized by Lopez et al. in his studies of the autolytic enzyme (Ronda et al. (1987) Eur. J. Biochem, 164:621-624). Other proteins containing this domain include the autolysin of the pneumococcal phage and the protective antigen, pneumococcal surface protein A (PspA) (Ronda, C. et al. (1987) Eur. J Biochem, 164:621-624 and McDaniel, L. S., et al. (1992)Microb Pathog, 13:261-269). CbpA, fails to colonize the nasopharynx domain which is shared with its other family members C terminus) but its activity of binding to human cells arises from its unique N-terminal domain. Since the process of colonization and the progression to disease depend on pneumococcal attachment to human cells as a primary step, interruption of the function of the N terminal domain, either by cross reactive antibody or by competitive inhibition with a peptide mimicking this domain, may be critical to blocking disease.
Choline binding proteins for anti-pneumococcal vaccines are discussed in PCT International Application No. PCT/US97107198 and such PCT Application is incorporated in its entirety by reference. Current vaccines against S. pneumoniae employ purified carbohydrates of the capsules of the 23 most common serotypes of this bacterium, but such vaccine is only 50% protective (Shapiro et al. NJEM 325:1453, 1991) and is not immunogenic under the age of 2. Further, a therapeutic polypeptide would offer a therapeutic option in cases of infection with multi resistant organisms. Therefore, the invention herein fills a long felt need by providing a protective vaccines.